In fluidized-bed, olefin polymerization reactors, fluidization of the bed is achieved by means of upward flowing gas that also serves to remove some of the heat of reaction. In the “condensed mode” of operation, the fluidizing gas contains a condensable component which increases the cooling capacity available within the reactor. A grid at the bottom of the reactor is used to uniformly distribute the fluidization gas across the reactor cross-section and to prevent solids from entering the gas supply plenum.
This grid is known by various names in the art such as “gas distributing plate,” “gas distribution plate,” “gas distributor plate,” “perforated plate,” “gas distribution grid,” “gas fluidization grid,” and “gas dispersion grid”.
Polymer powder in the reactor can sometimes fuse together, which can lead to the formation of polymer sheets on the reactor walls and/or agglomerates (chunks) on the gas distribution grid. Sheets that break off the wall and settle on the grid can be a precursor for the formation of agglomerates on the grid. Blockage of the gas flow through the grid due to the presence of agglomerates adversely affects the hydrodynamics of the fluidized bed, including the partial or total loss of bed fluidization. When fluidization is lost in portions of the bed, the ability to effectively remove the heat from the polymer particles is also lost. This can lead to melting of the polymer and fusing of the polymer particles into additional agglomerates or chunks. Alternatively, conditions in the polymerization reactor may be such that the cohesive forces in the powder are strong enough to fuse individual powder particles into agglomerates, causing local or total defluidization of the bed, loss of the ability to effectively cool the polymer, and in turn lead to the formation of agglomerates or chunks.
It is desirable, therefore, to have a means for detecting the presence and size of agglomerates and to have a means for breaking up any agglomerates or slowing the rate of their growth. If the growth of agglomerates appears to be out of control, a means for rapidly killing the reaction within the agglomerate, defluidized portions of the bed, and the rest of the powder bed would also be desirable.